JP2009125811A - Method for centrifugally casting highly reactive titanium metals - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for centrifugally casting a highly reactive titanium metal. <P>SOLUTION: The method for centrifugally casting a highly reactive titanium metal includes a step of providing a cold wall induction crucible having a plurality of induction coils and a removable bottom plate; a step of using a power source to heat a titanium metal charge in the induction crucible to obtain a molten metal; a step of preheating a secondary crucible and placing the preheated secondary crucible into a centrifugal casting machine; a step of positioning the centrifugal casting machine having the secondary crucible beneath the induction crucible; a step of withdrawing the bottom plate of the induction crucible and turning off the power source to the induction crucible to allow the molten metal to fall from the induction crucible into the secondary crucible; and a step of accelerating the secondary crucible to centrifugally force the molten metal into a casting mold to produce a cast component. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The embodiments described herein generally relate to a method for centrifugal casting of highly active metals. In particular, the examples herein generally describe a method for centrifugal casting of high activity titanium alloys, particularly titanium aluminide alloys.

  Turbine engine designers are searching for new materials with better properties that can reduce the weight of the engine and achieve higher engine operating temperatures. Titanium alloys (Ti alloys), particularly titanium aluminide-based alloys (TiAl alloys), have promising low-temperature mechanical properties such as room temperature ductility and toughness, and also have high intermediate temperature strength and creep resistance. For these reasons, TiAl alloys have the potential to replace nickel-based alloys currently used in many turbine engine components.

  Empty arc melting (VAR) is one of the techniques commonly used for melting Ti alloys. VAR generally includes a step of arcing between a titanium alloy electrode and a titanium alloy piece (eg, electrode piece) placed in a water-cooled copper crucible. A molten pool is formed and the electrodes are gradually dissolved. When sufficient molten metal is obtained, the electrodes are pulled out, the crucible is tilted, and the molten metal is poured into a mold for casting parts.

  The VAR method has several drawbacks. Titanium electrodes used in the VAR process are expensive due to the high billet / forging material of titanium and the labor required to create electrodes with scrap or recycled materials according to the standard, It will be expensive. In addition, due to the standard regarding the pre-alloy electrode, production of non-standard alloy becomes difficult and expensive. Furthermore, the need to use a water-cooled crucible reduces the metal superheat limit, which further affects fluidity and makes it difficult to pour thin castings. Further, a high temperature gradient is generated in the molten metal with the maximum temperature at the contact position between the arc and the metal. This also affects the pouring of the mold and may cause an undesirable temperature gradient in the solidified casting.

  In view of the above-mentioned problems related to the VAR method, there is a vacuum induction melting (VIM) method as another method used when the Ti alloy is melted. VIM has been developed to process special and special alloys that contain active elements such as titanium and aluminum and that cannot be melted and cast in air. As the use of such alloys continues to increase, VIM is becoming increasingly common.

  Vacuum induction melting generally involves heating the metal in a crucible made of a refractory non-conductive alloy oxide until the charge metal in the crucible is dissolved in a liquid state. In this technique, solid titanium alloy pieces are typically placed in a cooled metal hearth made of copper and melted in an inert atmosphere using a very powerful heat source such as an arc or plasma. While a molten pool is first formed in and on the top of the charged titanium, the titanium adjacent to the closed wall of the copper hearth remains solid. The formed solid titanium “skull” contains pure liquid titanium metal. For a general discussion of cold wall induced melting, see US Pat.

  For many reasons as described above, copper crucibles are most commonly used for cold wall induction melting of highly active alloys. For example, in the case of a ceramic crucible, cracks may occur in the crucible if the crucible is subjected to high thermal stresses during melting and casting. Such cracking shortens the life of the crucible and creates the possibility of foreign matter entering the part being cast. Furthermore, the ceramic crucible may be damaged by the highly active TiAl alloy, and the titanium alloy may be impure due to both the refractory alloy made of oxide and oxygen. Similarly, when a graphite crucible is used, a large amount of carbon is mixed into the titanium aluminide from the crucible and the titanium alloy is impure. Such impureness causes a loss of mechanical properties of the titanium alloy.

  Copper is less likely to present the above-mentioned problems with ceramics and graphite crucibles, and copper crucibles are generally used for melting highly active alloys by cold wall induction melting.

  However, melting a low temperature crucible in a copper crucible has the metallurgical advantages in the processing of high activity alloys as described above, but it has a low superheat limit, yield loss due to skull formation and high power requirements. There are numerous technical and economic restrictions to do. In particular, in a cold wall induction crucible, when the application of electric power to the crucible is stopped and the metal approaches the water-cooled copper side of the mold, heat loss occurs.

  One form that has been developed and used to address the above-mentioned problems associated with vacuum induction melting is subcast casting through a nozzle from a cryogenic furnace melting system. See U.S. Pat. Nos. 5,099,049 to Rowe and U.S. Pat. The commonly used nozzle material is copper or brass, which is suitable as a heat conducting material, but it is described here that graphite and heat insulating materials are also used as the nozzle material.

  Using nozzles offers many advantages over other common practices, but does not completely eliminate complex problems. For example, in low-temperature hearth melting and subcast casting of an active metal such as titanium, there is a case where the molten metal condenses and clogs the nozzle. In addition, in many crucible / nozzle devices, considerable effort is required to desirably control liquid flow, minimize nozzle erosion, and minimize melt depletion.

Another form that has been developed and used to address the above-mentioned problems associated with vacuum induction melting is levitation melting that typically involves the use of energy from an induction coil to electromagnetically levitate the melting metal . For a general discussion of levitation dissolution, see US Pat. However, the induction magnetic field can both heat the metal and hold the molten metal that floats in the crucible space. It will cool down again. Thereby, there exists a possibility that the metal mold may be poured into the mold inconveniently.
US Pat. No. 4,654,858 US Pat. No. 5,164,097 US Pat. No. 5,275,229 US Pat. No. 6,776,214 US Pat. No. 5,060,914

  In view of such progress, to improve the melting method of highly active alloys such as TiAl so as to keep the alloy molten during pouring and reduce the problems associated with the conventional melting method Is required.

  Embodiments herein are generally methods for centrifugal casting of highly active titanium metal, comprising providing a cold wall induction crucible having a plurality of induction coils and a removable bottom plate, and using a power source to provide the induction crucible. Heating the charged titanium metal inside to obtain a molten metal, preheating the secondary crucible, placing the preheated secondary crucible in a centrifugal casting machine, and the centrifugal casting having the secondary crucible Disposing a machine under the induction crucible, pulling out the bottom plate of the induction crucible, turning off the power to the induction crucible, and dropping the molten metal from the induction crucible into the secondary crucible And producing a cast part by applying centrifugal force by rotating the secondary crucible at an accelerated speed to flow the molten metal into a mold. .

  Further, embodiments herein are generally methods for centrifugal casting of highly active titanium metal, comprising providing a cold wall induction crucible having a plurality of induction coils and a removable bottom plate; Heating the charged titanium metal in the induction crucible to obtain a molten metal; preheating the secondary crucible; placing the preheated secondary crucible in a centrifugal casting machine; and a funnel under the induction crucible Disposing the centrifugal casting machine having the secondary crucible under the funnel, pulling out the bottom plate of the induction crucible and turning off the power to the induction crucible, Dropping the molten metal from the induction crucible into the secondary crucible through the funnel, and centrifugally applying the centrifugal force by rotating the secondary crucible at an accelerated speed in the mold. Centrifugal casting method comprising the steps of producing a cast component flowing to about.

  Still further, embodiments herein are generally methods for centrifugal casting of high activity titanium aluminides, comprising providing a cold wall induction crucible having a plurality of induction coils and a slidably removable bottom plate; Heating the charged titanium aluminide in the induction crucible using a power source to obtain a molten titanium aluminide; preheating the secondary crucible and placing the preheated secondary crucible in a centrifugal casting machine; Disposing a niobium funnel under the induction crucible; disposing the centrifugal casting machine having the secondary crucible under the niobium funnel; and slidingly removing the bottom plate of the induction crucible. In addition, the power to the induction crucible is turned off, and the molten titanium aluminide is transferred from the induction crucible into the secondary crucible through the niobium funnel. Holding the secondary crucible stationary for about 0.5 to about 2 seconds after the molten titanium aluminide falls into the secondary crucible, and rotating the secondary crucible for about 1 second The present invention relates to a centrifugal casting method comprising a step of producing a low-pressure turbine blade by applying centrifugal force to flow the molten titanium aluminide into a mold by accelerating to about 100 rpm to about 600 rpm within about 2 seconds.

  These and other features, aspects, and advantages will become apparent to those skilled in the art from the following disclosure.

  The embodiments described herein generally relate to a method of centrifugally casting a highly active metal, particularly a titanium alloy and a titanium aluminide alloy, to obtain a net shape part, but the following description should be limited to this. is not.

  According to the following description of the present specification, a cold wall induction crucible 10 having a body 12 is prepared as shown in FIG. The body 12 is made of some metal having good thermal conductivity and conductivity, such as copper. The body 12 is water cooled to prevent the copper from dissolving when the crucible is heated. Specifically, copper generally melts at about 1900 ° F. (about 1038 ° C.), TiAl dissolves at about 2600 ° F. (about 1427 ° C.), and the copper in the crucible is coexisting with titanium at a low melting point. A molten mixture is formed. These can be prevented by water cooling the crucible. Water cooling inlet 24 and outlet 26 can be used to circulate cooling water through a plurality of channels 28 disposed around body 12. The body 12 may have any desired shape applicable to induction melting, but in one embodiment, the body 12 is generally shaped as a hollow cylinder. Around the main body 12, a plurality of induction coils 14 that are heated using a power source 21 are arranged. The coil 14 serves as a heat source and melts the charge metal placed in the crucible and maintains its molten state, as will be described herein below.

  Further, the crucible 10 may have a removable bottom plate 16 shown in FIG. Similar to the crucible 10, the bottom plate 16 may be made of any metal having good thermal conductivity and conductivity, but in one embodiment is made of copper. The bottom plate 16 is also water-cooled, and a plurality of induction coils 14 are disposed below it. The induction coils 14 help melt the metal charged in the crucible 10 and maintain its molten state. In addition, an electrical insulating plate 19 constitutes the outer surface of the bottom plate 16 and helps maintain heat at the bottom of the crucible 10. As described herein below, the base plate 16 can be removed from the body 12 in a variety of ways including, but not limited to, sliding (shown in FIGS. 2 and 3), rotation, and dropping off.

  In use, a charge metal 18 comprising a highly active alloy is disposed within the body 12 of the crucible 10 as shown in FIG. In one embodiment, the charge metal 18 is made of a titanium alloy, particularly a titanium aluminide alloy, and includes, but is not limited to, agglomerates, ingots, granules, plates, powders, and combinations thereof. And can take any acceptable form. One skilled in the art will appreciate that the amount of metal 18 charged into the crucible 10 will vary depending on the intended application, but in one embodiment from about 1 pound (about 454 grams) to about 3 .5 pounds (about 1588 grams), and in other embodiments from about 1.25 pounds (about 567 grams) to about 3.3 pounds (about 1497 grams) of charge metal 18 is used herein. A net-shaped low-pressure turbine blade is produced as described below.

  Once the charge metal 18 is placed in the crucible 10, in one embodiment, a lid 20 made of the same metal as the crucible 10 is placed on top of the body 12 and is in position using the lid ring 22. To ensure that the crucible 10 is sealed. When the power supply 21 is turned on, the charge metal 18 melts when it reaches a suitable temperature, which in one embodiment is about 2700 ° F. to about 2835 ° F. (about 1480 ° C. to about 1557 ° C.). Those skilled in the art will appreciate that when a magnetic field is applied by an induction coil, the charge metal spontaneously heats due to resistive heating by the current in the charge metal. When the charged metal 18 begins to melt, the resulting molten metal 30 floats within the body 12 of the crucible 10 and the molten metal 30 contacts the inside of the body 12 as long as power is supplied to the crucible 10. Never do. The float of the molten metal 30 prevents the formation of a skull.

  Simultaneously with the melting of the charge metal in the induction crucible 10, the secondary crucible 32 or other similar holding device is preheated using any acceptable means such as, but not limited to, microwave or radiant energy. The The secondary crucible is made of graphite or ceramic and optionally has a metal liner such as niobium. The secondary crucible 32 serves to transfer the molten metal to the mold without losing any superheated state of the molten metal that occurs during induction melting in the induction crucible 10. In particular, the secondary crucible 32, when made of niobium, is at least about 1832 ° F. (about 1000 ° C.), and in one embodiment about 1832 ° F. to about 2200 ° F. (1000 ° C. to about 1200 ° C.). In the case of ceramic, it is preheated to at least about 1980 ° F. (about 1082 ° C.), and in one embodiment about 1980 ° F. to about 2400 ° F. (1082 ° C. to about 1316 ° C.). Preheating prevents thermal shock and cracking of the secondary crucible 32 so that the crucible can be reused. The preheated secondary crucible 32 is then attached to the rotating arm 34 of the centrifugal caster 36 and placed under the induction crucible 10 as schematically shown in FIG. For example, any conventional centrifugal casting machine such as Linn High-Therm Titancast 700 manufactured by Lin Hightherm (Germany) or Supercast (SEIT Supercast) manufactured by SEIT (Italy) is applicable to the present invention. .

  The removable bottom plate 16 is then withdrawn from the body 12 of the crucible 10 as described above. 2 and 3, the bottom plate 16 is slidably removed from the crucible 10 using any acceptable mechanism such as but not limited to a track or guide. Although the bottom plate 16 is removed, the molten metal 30 is maintained in a floating state in the main body 12 of the crucible 10 by the magnetic field generated by the induction coil 14 until further processing as shown in FIG.

  When the power source 21 is turned off, the molten metal 30 falls into the preheated secondary crucible 32. The secondary crucible 32 is kept stationary in the casting machine 36 for a length of time until the molten metal 30 completes movement from the induction crucible 10 through the niobium funnel 33 into the secondary crucible 32. This length of time is about 0.5 to about 2 seconds in one embodiment. Once the movement of the molten metal 30 is completed, the secondary crucible 32 is rapidly accelerated (about 1 to about 2 seconds) from about 100 rpm to a full speed of about 600 rpm. The casting machine 36 applies centrifugal force to the molten metal 30 and sends the molten metal 30 from the secondary crucible 32 into the mold 38 through a port 40 formed of at least one of a slit, a hole, a tube, or a combination thereof. . In this way, by quickly moving the molten metal 30 from the secondary crucible 32 to the mold 38, the contact time between them becomes less than about 5 seconds. By shortening the contact time, not only the heat loss is remarkably reduced, but also the problem of inadvertent reaction between the graphite or ceramic used in the construction of the secondary crucible 32 and the molten metal can be surely solved.

  The mold 38 may comprise any ceramic investment casting system with an inert surface coating and a thermally insulating backside material. As an example, in one embodiment, the template 38 includes a surface coating that includes an oxide. As used herein, the term “oxide” refers to a composition selected from the group consisting of scandium oxide, yttrium oxide, hafnium oxide, lanthanoid oxide, and combinations thereof. In addition, lanthanide oxides (also known as “rare earth” compositions) include lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, promethium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, It consists of an oxide selected from the group consisting of erbium oxide, ytterbium oxide, lutetium oxide and combinations thereof. The mold 38 includes a back side that includes a refractory material selected from the group consisting of aluminum oxide, zirconium silicate, silicon dioxide, and combinations thereof in a colloidal silica suspension.

  Once the molten metal has substantially moved into the mold 38, the centrifugal casting machine 36 is turned off. The resulting part, in one embodiment, the low pressure turbine blade 42 shown in FIG. 4, is removed from the mold 38 using conventional methods. Since it is based on centrifugal casting, the blades 42 require little processing after casting. The centrifugal force generated by the casting machine 36 makes it easy to pour even a thin part of the mold, and optimally pours into the mold 38. As a result, a net shape part can be obtained.

  Furthermore, since a cold wall crucible is used for melting the charged metal, the thermal stress on the crucible is reduced and cracking of the crucible is reduced. Thereby, while being able to reuse a crucible, the foreign material mixing in a casting component can be reduced. In addition, since the contact between the molten metal and the secondary crucible is limited, the possibility that the molten metal is impure due to breakage of the crucible is reduced. It becomes difficult to impure the molten metal, which leads to an improvement in the mechanical properties of the titanium alloy.

  This written description discloses the invention using examples, including the best mode, and also enables those skilled in the art to implement and utilize the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Where such other examples have structural elements that do not differ from the language of the claims, or include equivalent structural elements that have only minor differences from the language of the claims, Within the scope of the following claims.

1 is a schematic cross-sectional view of one embodiment of a cold wall induction crucible charged with metal, in accordance with the description herein. FIG. FIG. 6 is a schematic cross-sectional view of one embodiment of a cold wall induction crucible with the bottom plate removed and the molten metal floating inside according to the description herein. 1 is a schematic cross-sectional view of one embodiment of a centrifugal casting system in accordance with the description herein. 1 is a schematic perspective view of one embodiment of a low pressure turbine blade that is a part cast according to the description herein; FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cold wall induction crucible 12 Main body 14 Coil 16 Removable bottom plate 18 Charging metal 19 Electrical insulating plate 20 Lid 21 Power supply 22 Lid ring 24 Water cooling inlet 26 Water cooling outlet 28 Channel 30 Molten metal 32 Secondary crucible 33 Funnel 34 Rotating arm 36 Casting Machine 38 Mold 40 Port 42 Low pressure turbine blade

Claims (20)

A highly active titanium metal centrifugal casting method comprising:
Providing a cold wall induction crucible having a plurality of induction coils and a removable bottom plate;
Heating the charged titanium metal in the induction crucible using a power source to obtain a molten metal;
Preheating a secondary crucible and placing the preheated secondary crucible in a centrifugal caster;
Placing the centrifugal caster with the secondary crucible under the induction crucible;
Pulling out the bottom plate of the induction crucible and turning off the power to the induction crucible to drop the molten metal from the induction crucible into the secondary crucible;
A method of producing a cast component by rotating the secondary crucible at an accelerated speed to apply centrifugal force to flow the molten metal into a mold.   The method of claim 1, wherein the charged titanium metal comprises a titanium aluminide alloy.   3. A method according to claim 1 or 2, comprising the step of withdrawing the bottom plate of the induction crucible using a method selected from the group consisting of sliding, rotating and falling off.   The method according to claim 1, wherein the cast part comprises a low-pressure turbine blade.   The method according to any one of claims 2 to 4, comprising heating the charged metal to a temperature of 1480 ° C to 1557 ° C using the induction coil of the induction crucible to obtain the molten metal.   The method according to claim 1, wherein the molten metal is floated inside the induction crucible.   Preheating the secondary crucible to a temperature of at least 1000 ° C if the secondary crucible is made of niobium, and preheating the secondary crucible to a temperature of at least 1082 ° C if the secondary crucible is made of china. Item 7. The method according to any one of Items 2 to 6. Keeping the secondary crucible stationary for 0.5 to 2 seconds after the molten metal has fallen into the secondary crucible;
Thereafter, the step of accelerating the rotation of the secondary crucible to 100 rpm to 600 rpm within 1 second to 2 seconds to apply centrifugal force to flow the molten metal into the mold. The method according to any one of the above.   The method according to any one of claims 1 to 8, wherein the template is made of an oxide selected from the group consisting of scandium oxide, yttrium oxide, hafnium oxide, lanthanoid oxide, and combinations thereof. A highly active titanium metal centrifugal casting method comprising:
Providing a cold wall induction crucible having a plurality of induction coils and a removable bottom plate;
Heating the charged titanium metal in the crucible using a power source to obtain a molten metal;
Preheating a secondary crucible and placing the preheated secondary crucible in a centrifugal caster;
Placing a funnel under the induction crucible;
Placing the centrifugal caster with the secondary crucible under the funnel;
Pulling out the bottom plate of the induction crucible, turning off the power to the induction crucible, and dropping the molten metal from the induction crucible through the funnel into the secondary crucible;
A method of producing a cast component by rotating the secondary crucible at an accelerated speed to apply centrifugal force to flow the molten metal into a mold.   The method of claim 10, wherein the charged titanium metal comprises a titanium aluminide alloy.   12. A method according to claim 10 or 11, comprising the step of withdrawing the bottom plate of the induction crucible using a method selected from the group consisting of sliding, rotating and falling off.   13. A method according to any one of claims 10 to 12, wherein the cast part comprises a low pressure turbine blade.   14. The method according to claim 11, further comprising heating the charged metal to a temperature of 1480 ° C. to 1557 ° C. using the induction coil of the induction crucible to obtain the molten metal.   The method according to claim 10, wherein the molten metal is floated in the induction crucible.   Preheating the secondary crucible to a temperature of at least 1000 ° C if the secondary crucible is made of niobium, and preheating the secondary crucible to a temperature of at least 1082 ° C if the secondary crucible is made of china. Item 16. The method according to any one of Items 11 to 15. Keeping the secondary crucible stationary for 0.5 to 2 seconds after the molten metal has fallen into the secondary crucible;
The method further comprises the step of applying centrifugal force to flow the molten metal into the mold by accelerating the rotation of the secondary crucible to 100 rpm to 600 rpm within 1 second to 2 seconds. The method according to any one of the above. A method for centrifugal casting of highly active titanium aluminide comprising:
Providing a cold wall induction crucible having a plurality of induction coils and a slidably removable bottom plate;
Heating the charged titanium aluminide in the crucible using a power source to obtain molten titanium aluminide;
Preheating a secondary crucible and placing the preheated secondary crucible in a centrifugal caster;
Placing a niobium funnel under the induction crucible;
Placing the centrifugal caster with the secondary crucible under the niobium funnel;
The bottom plate of the induction crucible is slidably removed, the power to the induction crucible is turned off, and the molten titanium aluminide is transferred from the induction crucible through the niobium funnel into the secondary crucible. Dropping the stage;
Keeping the secondary crucible stationary for 0.5 to 2 seconds after the molten titanium aluminide has dropped into the secondary crucible;
Thereafter, the rotation of the secondary crucible is accelerated to 100 rpm to 600 rpm within 1 second to 2 seconds, thereby applying the centrifugal force to flow the molten titanium aluminide into the mold and casting the low pressure turbine blade. A method consisting of   The method according to claim 18, further comprising heating the charged metal to 1480 ° C. to 1557 ° C. using the induction coil of the induction crucible to obtain the molten metal.   Preheating the secondary crucible to a temperature of at least 1000 ° C if the secondary crucible is made of niobium, and preheating the secondary crucible to a temperature of at least 1082 ° C if the secondary crucible is made of china. Item 20. The method according to Item 19.

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